Amp gauge not working now

My amp gauge now is not working after I did a parallel 8 gauge wire from the alternator to the started relay stud. I would have thought that it would still work since it is getting voltage through it.
I guess my question is why it did not work? I will probably just disconnect it and splice the wires together. I drove the car and noticed it was not working, so I got concerned that the battery was not charging. After my drive I checked the battery and it had 12.5 volt in it, so it was being charged.